Feed control for metal spray guns and the like



Oct. 10, 1961 s, RQNDEAU 3,003,702

FEED CONTROL FOR METAL SPRAY GUNS AND THE LIKE Filed Sept. 19, 1960 Pal.\\\\\W T 6 1 2 73 5 57 j 25 M r, 2 2 /6 I8 3 v V 77 6 M 5 j 26 3o 1 v14/fjf INVENTOR.

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United States Patent Ofiice 3,003,702 Patented Oct. 10, 1961 3,003,702FEED CONTROL FOR METAL SPRAY GUNS AND THE LIKE Henry S. Rondeau, 2865Coventry Road, Cleveland, Ohio Filed Sept. 19, 1960, Ser. No. 56,744 19Claims. (Cl. 239-84) This invention relates, as indicated, to a feedcontrol for metal spray guns and the like and more particularly to ametal spray gun of the wire feed type which will give uniformatomization of the wire continually regardless of varying air pressures,imperfections in the wire, and fluctuations in the gas flame.

In metal spray guns wherein the usual gases, e.g., acetylene, oxygen andair are fed to a chamber together with the metal in wire form to besprayed, the Wire feed mechanism may be driven as by an air motorconnected with the air supply source. The turbine of such air motordrives feed rollers contacting the wire thus moving it into thecombustion chamber. The melted Wire is sprayed by the flame and hotgases through the discharge nozzle of the gun. However, since thediameter of the discharge orifice of the nozzle is only slightly largerthan the diameter of the wire, the improper feed of the wire withrelation to the atomization of the tip thereof can cause pulsations,spattering, and other irregularities in the metal spray obtained.Obviously, if the wire is fed into the nozzle at an excessive linealspeed, it will not be completely melted whereby the resulting spray willinclude large unmelted particles and, on the other hand, if the wire isfed into the nozzle at an insufficient lineal speed, the productivecapacity of the gun will suffer and furthermore may result inback-firing and sticking of the wire due to accumulation of metal at thenozzle tip and gas jets. Heretofore, manual controls of both the gaspressure and wire feed rate have been employed with the skill of theoperator determining the most desirable conditions.

It is accordingly a principal object of the present invention to providea feed mechanism for metal spray guns which will give uniformatomization at all times.

It is another object of the present invention to provide a metal spraygun of the wire feed type which will maintain the advancing melted-downconical tip of the wire in the portion of the nozzle at which mostuniform and efficient melting and spraying is achieved.

It is yet another object of the present invention to provide a metalspray gun of the wire feed type which will give uniform resultsregardless of Varying air pressures, imperfections in the Wire, andfluctuations in the fusing flame.

Other objects and advantages of the present invention will becomeapparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims, the following description andthe annexed drawings setting forth in detail a certain illustrativeembodiment of the invention, this being indicative, however, of but oneof the various ways in which the principles of the invention may beemployed.

In said annexed drawing:

FIG. 1 is a perspective View of a metal spray gun of the wire feed typein accordance with the present invention; and

FIG. 2 is a diagrammatic fragmentary sectional view of the feed controlfor such gun in accordance with the present invention.

Referring now to the annexed drawing and especially to FIG. 1, it willbe seen that a metal spray gun of the wire feed type is provided whereina wire is fed through two feed rollers 1 and 2 mounted for rotation onvertically extending axes and therefrom into a gas head 3. Such feedrollers 1 and 2 and the gas head 3 are mounted on a housing 4 which maybe manually held or mounted on a fixture to have the gas head and metalspray issuing from the orifice 5 directed at the Work to be coated withthe metallic spray. In order to melt or fuse the Wire W which is fedinto the gas head 3, such gas head is supplied with a combustible gas, acombustion supporting gas, such as oxygen, and a blast gas such ascompressed air. A typical combustion gas would be acetylene with thecombustion supporting gas oxygen supplying an oxyacetylene flame to meltor fuse the tip 6 of the wire W to be sprayed through the orifice 5 bythe blast gas or compressed air. A conical nozzle 7 may be secured as bynut 8 concentrically of the gas head 3 and such nozzle is provided withinlets 9 and 10 for the combustible gas and the combustion supportinggas. The blast gas or compressed air enters through passage 11 and flowsinto the gas head through several orifices such as that shown at 12. Abranch passage 13 leads from the passage 11 through-pilot valve 14 andcontrol valve 15 to motor 16. The motor 16 is in the form of a gasturbine effective to drive the shaft 17 and suitable gearing 18vertically oppositely to rotate feed rolls 1 and 2 through shafts 19,thus feeding the Wire W therebetween into the gas head 3 to be sprayedthrough orifice 5.

A suitable plug valve 2% may be provided with control handle 21simultaneously to govern the flow of the combustible gas through thepassage 9, the combustion supporting gas through the passage Ill, andthe blast gas through the passage 11. The inlets for these variouspassages may be provided at the bottom of vertically extending supportor handle 22 as shown at 23. The valve 15 may be manually operated thuscontrolling the amount of air passing through the branch passage 13 tothe motor 16 and thus the rate of feed of the wire W. Manual adjustmentsof the valves 20 and 15 will produce initially the proper spray from theorifice 5. However, fiuctuations in the wire make-up, the pressure ofthe compressed air or oxyacetylene gases, will vary the set or desiredatomized spray of the metal wire and heretofore only a manual adjustmentcould alleviate the difficulty incurred.

It will be apparent that if the wire tip 6 extends further to the rightas seen in FIG. 2, such wire will tend to block the orifice 5 thuscreating a higher back pressure in the combustion chamber 25 Within thegas head 3. Likewise, as the tip of the wire 6 moves to the left awayfrom the orifice 5, the pressure within chamber 25 will drop. It hasbeen found that the variation in the pressure in chamber 25 can be fedback to the motor 16 properly to control the feed of wire W and thus theposition of tip 6 with respect to the center of the flame and theorifice 5 to obtain a uniform and proper atomization of the wire.

In order to obtain this feedback, the pilot type diaphragm valve 14 isprovided which opens or closes with the increase or decrease of the airpressure in the chamber 25. Such pilot type diaphragm valve may includethree plates 25, 27 and 28, with the branch passage 13 extending throughthe plate 26 beneath ridge 29. The main diaphragm 30' is secured betweenplates 26 and 27 and overlies an aperture 31 in plate 27 directlybeneath ridge 29.

Secured between the plates 27 and 28 is a secondary diaphragm 32 havinga plastic member 33 secured thereto having a central upstanding portion34 fitting within orifice or aperture 31 adapted to move and pressdiaphragm 30 toward ridge 29 restricting fluid flow within passage 13. Achamber 35 is provided between the plates -27 and 28 to allow forvertical movement of the diaphragm 32 and member 33 therein. The pilotchamber beneath the diaphragm is connected directly to the chamber 25 inthe gas head through passage 36. An adjustable bleeder valve 37 havingadjusting screw 38 is provided in the pilot passage 36 to exhaust air toatmosphere through orifice 39 to control the pressure Within pilotpassage 36. This actuation of the pilot bleeder valve will control theactuation of the pilot valve to obtain the fine adjustments desired inthe relation between the blast gas flow and the rate of feed of the wireW. It can now be seen that the pressure within the chamber 25 and thusthe pressure in the lower portion of pilot cavity 35 beneath therelatively large area diaphragm 32 will cause vertical movement of themember 34 to control the fluid flow in branch passage 13, and thus thespeed of turbine motor 16. Accordingly, the pointed end of the wire Witself acts as a valve needle when it goes forward through the nozzleinto the orifice setting up a back pressure causing the pilot valve toreduce the fluid flow through branch passage d3 slowing down motor 16and thus the rate of feed of the wire. The motor 16, of course, willslow down, moving the melted down tip 6 of the wire W away from theorifice 5 reducing the pressure in the chamber 25 and thus opening thevalve 14. If, however, the wire pilot recedes too far from the airorifice 5, the back pressure in the chamber 25 will decrease and thistime the valve 14 will open permitting more air to increase the turbinespeed thus causing the Wire feed to speed up again and adjust itselfinto the center of the flame. if desired, a small orifice 40 may beemployed to interconnect branch passage 13 and pilot conduit 36preventing undue oscillations or sharp fluctuations in the operation ofthe valve.

It can now be seen that there has been provided an inverse feedbackcontrolling the rate of feed of the wire W in response to the pressurewithin the chamber 25. Accordingly, the higher the back pressure inchamber 25, the slower the rate of feed of the wire W and inversely, thelower the back pressure in chamber 25, the higher the rate of feed ofthe wire W. With this type of device, closer and automatic control ofthe wire feed is obtained so that it cannot spray beyond the center ofthe flame and will give uniform atomization at all'times. This mechanismmakes allowance for variations in air pressures, imperfections in thewire which create drag, and fluctuations in the oxyacetylene flame.

The spray Wire W employed in guns of this type may be steel, alloys ofsteel, bronze, aluminum, brass, and such metals may be used for coating,molding or bonding purposes. Wires of this type may be made of powderedor granulated metal held together by a plastic bond which easilydisintegrates in the hot flame produced by the combustible andcombustion supporting gases.

Whereas the invention has been illustrated as applied to a metal spraygun of the wire feed type, it will be readily understood that it isequally applicable to a spray gun for ceramic rod or to a spray gun ofthe powder feed type with the pressure in chamber 25 regulating andcontrolling the amount of powdered metal fed into the combustionchamber.

Other modes of applying the principles of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims or the equivalent of suchbe employed.

1, therefore, particularly point out and distinctly claim as myinvention:

1. A metal spray gun comprising a combustion chamber having a dischargemetal spray orifice, means to feed metal into said chamber to be fusedtherein and sprayed through such discharge orifice; and inverse feedbackmeans responsive to the pressure in said combustion chamber to controlthe rate of feed of said metal into Said chamber.

2. A metal spray gun as set forth in claim 1 including a blast gasconduit leading to said combustion chamber, and a branch conduit leadingfrom said blast gas conduit to a gas turbine, said gas turbine drivingsaid means to feed metal to said combustion chamber, said inversefeedback means controlling the passage of gas in said branch conduit.

3. A metal spray gun as set forth in claim 2 wherein said inversefeedback means comprises a pilot valve in said branch conduit, and meansto open and close said pilot valve in response to the pressure in saidcombustion chamber.

4. A metal spray gun as set forth in claim 3 wherein said pilot valveincludes two diaphragms, one said diaphragm controlling gas flow in saidbranch conduit in response to movement of the other said diaphragm.

5. A metal spray gun as set forth in claim 4 wherein the other saiddiaphragm has a large area exposed to a pilot chamber, the pilot conduitmeans interconnecting said pilot chamber and said combustion chamber.

6. A metal spray gun as set forth in claim 5 including substantiallyrigid plastic plate means interposed between said diaphragms.

7. A metal spray gun as set forth in claim 5 including a bleeder valvein said pilot conduit to bleed said pilot conduit to atmosphere.

8. A metal spray gun of the wire feed type comprising a combustionchamber having a discharge metal spray orifice, means to feed a wireinto said chamber to be fused therein and sprayed through such orifice;and inverse feedback means responsive to the gas pressure in saidchamber to control the rate of feed of said wire into said chamber.

9. A metal spray gun as set forth in claim 8 including feed rollers forsaid wire driven by a gas turbine, a gas supply to said combustionchamber, and branch conduit means leading from said gas supply to saidgas turbine, said inverse feedback means controlling the flow of gas insaid branch conduit thus to control the rate of feed of said wire.

10. A metal spray gun as set forth in claim 9 wherein said inversefeedback means comprises a pilot valve in said branch conduit to controlthe flow in said branch conduit, and means to open said pilot valve inresponse to a drop in pressure in said combustion chamber and to closesaid pilot valve in response to an increase in pressure in saidcombustion chamber.

11. A metal spray gun as set forth in claim 8 wherein said combustionchamber is frusto-conical in shape, said discharge orifice being at thesmall end thereof, and said orifice being of a diameter only slightlylarger than the diameter of said wire.

12. A metal spray gun as set forth in claim 11 including means to supplya combustible and combustion supporting gas to said combustion chamber.

13. A metal spray gun of the wire feed type comprising a combustionchamber having a flame therein with a discharge metal spray orifice,means to feed a wire into said combustion chamber to be fused thereinand sprayed through such orifice; and means responsive to the positionof the tip of said wire in said combustion chamber to control the rateof feed of said wire into said chamber thereby to maintain the tip ofsaid wire in the center of said flame to obtain a substantially uniformatomization of said wire in said combustion chamber.

14. In a metal spray gun of the wire feed type having a combustionchamber into which wire is fed to be melted and sprayed therefrom; meansinversely to vary the rate of feed of said wire in relation to thepressure in said combustion chamber.

15. The combination set forth in claim 14 wherein said wire is fed byfeed rolls driven by a turbine motor, and means inversely to control therate of feed of said turbine motor in relation to the pressure in saidcombustion chamber.

16. In a metal spray gun of the type having a conical combustion chamberinto which wire to be melted therein is fed and sprayed through anorifice at the smaller end thereof, means to supply such combustionchamber with a combustible gas, a combustion supporting gas, and a blastgas for forcing the atomized metal through such orifice, turbine drivenmeans feeding said Wire to said combustion chamber, said turbine drivenmeans being driven by a branch passage leading from the blast gasconduit leading to said combustion chamber; and pilot valve means insaid branch passage controlling the speed of said turbine motor, andmeans interconnecting said pilot valve and said combustion chamberthereby inversely to vary the rate of feed of the Wire with respect tothe pressure in said combustion chamber.

17. The combination set forth in claim 16 wherein said pilot valveincludes a main diaphragm adapted to block the flow of fluid in saidbranch passage, 21 secondary diaphragm movable in response to thepressure in said combustion chamber.

18. The combination set forth in claim 17 wherein said wire is fed tosuch combustion chamber by juxtaposed feed rolls adapted to rotate aboutvertical axes, said feed rolls being driven through suitable gearing bysaid turbine motor.

19. The combination set forth in claim 18 including a manuallyadjustable valve in said branch passage thereby manually to control thespeed of said turbine motor.

References Cited in the tile of this patent UNITED STATES PATENTS1,262,134 Stolle Apr. 9, 1918 FOREIGN PATENTS 821,558 Great Britain Oct.7, 1959

